I backed up the PVM. Deleted all the snapshots. Made the HDD larger in Configuration. Expanded my available C: drive space to 18 GB. Then, after 10 separate failures, I was finally able to upgrade to Windows 10 Creator edition and all current security patches. If this were a standalone Windows laptop, it would have been easy. Parallels gets in the way over and over, because of its lousy design and lack of transparency telling us what is taking up the space in our PVMs. Don't bother writing to Parallels Technical Support for help on any of this. You get obscure email replies that read like they came out of Google Translate in broken, incomprehensible English.